The present invention relates to a device for control of an aerodynamic steering surface, such as a fin flap or an all-moving fin, of a helicopter. It also relates to a helicopter equipped with such a control device.
It is known, in a helicopter provided with a single main rotor providing lift and propulsion, that the fuselage has a tendency, in reaction to the torque exerted by said main rotor, to turn in the direction opposite to the direction of rotation thereof. It is known, moreover, that in order to combat the reaction torque to which the fuselage is subjected, it is usual to provide an auxiliary anti-torque rotor, capable of generating a transverse thrust and driven in rotation from the motive power source of the main rotor. Thus, the anti-torque auxiliary rotor picks off some of the power from this motive power source.
Another drawback of an anti-torque rotor lies in its induced drag, which may amount to half the thrust at high speeds, as well as in the induced noise which is liable to be very troublesome.
It results therefrom that, for the performance of the helicopter, it is advantageous for the anti-torque auxiliary rotor to be assisted in its function of anti-torque lateral stabilization of the fuselage.
As is set out, for example, in the patent U.S. Pat. No. 2,818,224, it is possible, to that end, to lighten the load on said anti-torque rotor, in translation flight, with the aid of an aerodynamic thrust being exerted on a fin provided at the rear of said helicopter. Such a thrust is usually obtained by choosing a cambered profile for the fin, and by setting the fin at a certain angle with respect to the plane of symmetry of the fuselage. However, for a fixed fin definition, the thrust thus obtained when the helicopter is flying at zero sideslip depends only on the dynamic pressure of the air on the fin and is therefore not variable. As the anti-torque force to be exerted varies in a different way as a function of speed, as well as as a function of other flight parameters, it results therefrom that the optimum load lightening for the anti-torque rotor is in practice possible only in a single set of flight conditions.
In order to avoid the drawbacks and limitations appearing in the use of such a fixed load-lightening fin, a fin flap can be employed, which is adjustable in terms of orientation.
The present invention applies exclusively to a helicopter equipped with a compound anti-torque system comprising:
an anti-torque auxiliary rotor, controllable and exerting an anti-torque lateral thrust ; and PA0 an aerodynamic steering surface (a fin flap for example), controllable and generating anti-torque transverse lift. PA0 an anti-torque auxiliary rotor, controllable and exerting an anti-torque lateral thrust ; and PA0 said aerodynamic steering surface, controllable and generating an anti-torque transverse lift, PA0 either be representative of the action exerted by a pilot of the helicopter on a rudder pedal, which makes it possible to fit the device in accordance with the invention onto an ordinary helicopter with a mechanical flight control system ; PA0 or be determined by a calculating unit, from actions exerted respectively on a collective lever and on a rudder pedal by at least one pilot of the helicopter. PA0 first means, preferably including a potentiometer, for measuring the value of the displacement of said rod linkage, which is representative of said yaw control demand; PA0 second means for determining a control demand for the aerodynamic surface, from the value thus measured of the displacement of the rod linkage; and PA0 third means, preferably including an electric actuator or a motor, for actuating said aerodynamic surface in terms of speed, as a function of the control demand thus determined. PA0 means for determining said datum demand, as a function of the lateral load factor of the helicopter in such a way as to augment the lateral static stability of said helicopter; and/or PA0 means for rendering said control device inactive. PA0 a datum position of said rod linkage, from which said datum demand is determined; and/or PA0 the width of a dead control range, for which no control demand is forwarded to said third means for actuating the aerodynamic surface; and/or PA0 the width of an actuation range, for which said aerodynamic surface is actuated ; and/or PA0 the speed of actuation of said third means. PA0 means for indicating to said pilot of the helicopter the actual value of the angle of deflection of the aerodynamic surface ; and/or PA0 means for warning said pilot when said aerodynamic surface is in one of its two extreme deflection positions. PA0 a calculating unit, for determining a control demand for the aerodynamic surface, on the basis of the difference between the yaw control demand and the datum demand; and PA0 means for actuating said aerodynamic surface in terms of speed, as a function of the control demand thus determined.
As far as the principles of the control of such a fin flap are concerned, various flight control law concepts exist, known as deterministic concepts, that is to say which generate a deflection of the fin flap as a function of known flight condition parameters, this deflection being matched to the desired objective (according to a knowledge-based model). This control means, although useful in principle, is, by nature, not very robust as regards external aerodynamic changes (external carriage for example) and requires trimming in flight if the knowledge-based model turns out to be insufficiently accurate.
Moreover, the above-mentioned control means cannot generally be employed on every type of helicopter, or at the very least requires a modification, at least to the yaw control system of the helicopter.